Window.convertPointFromPageToNode

Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

Given a Point specified in the page's coordinate system, the Window method convertPointFromPageToNode() returns a Point object specifying the same location in the coordinate system of the specified DOM Node.

Please review the Browser compatibility section before using this method, as it's not widely supported (nor is the Point object it uses).